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    SubjectRe: [PATCH v3] mmc: sdhci-msm: Warn about overclocking SD/MMC
    Hi,

    On Thu, Dec 10, 2020 at 9:56 PM Adrian Hunter <adrian.hunter@intel.com> wrote:
    >
    > On 10/12/20 11:27 pm, Douglas Anderson wrote:
    > > As talked about in commit 5e4b7e82d497 ("clk: qcom: gcc-sdm845: Use
    > > floor ops for sdcc clks"), most clocks handled by the Qualcomm clock
    > > drivers are rounded _up_ by default instead of down. We should make
    > > sure SD/MMC clocks are always rounded down in the clock drivers.
    > > Let's add a warning in the Qualcomm SDHCI driver to help catch the
    > > problem.
    > >
    > > This would have saved a bunch of time [1].
    > >
    > > [1] http://lore.kernel.org/r/20201210102234.1.I096779f219625148900fc984dd0084ed1ba87c7f@changeid
    > >
    > > Suggested-by: Stephen Boyd <swboyd@chromium.org>
    > > Signed-off-by: Douglas Anderson <dianders@chromium.org>
    > > ---
    > >
    > > Changes in v3:
    > > - Proper printf format code.
    > >
    > > Changes in v2:
    > > - Store rate in unsigned long, not unsigned int.
    > > - Reuse the clk_get_rate() in the later print.
    > >
    > > drivers/mmc/host/sdhci-msm.c | 15 +++++++++++++--
    > > 1 file changed, 13 insertions(+), 2 deletions(-)
    > >
    > > diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
    > > index 3451eb325513..50beb407dbe9 100644
    > > --- a/drivers/mmc/host/sdhci-msm.c
    > > +++ b/drivers/mmc/host/sdhci-msm.c
    > > @@ -353,6 +353,7 @@ static void msm_set_clock_rate_for_bus_mode(struct sdhci_host *host,
    > > struct sdhci_msm_host *msm_host = sdhci_pltfm_priv(pltfm_host);
    > > struct mmc_ios curr_ios = host->mmc->ios;
    > > struct clk *core_clk = msm_host->bulk_clks[0].clk;
    > > + unsigned long achieved_rate;
    > > int rc;
    > >
    > > clock = msm_get_clock_rate_for_bus_mode(host, clock);
    > > @@ -363,10 +364,20 @@ static void msm_set_clock_rate_for_bus_mode(struct sdhci_host *host,
    > > curr_ios.timing);
    > > return;
    > > }
    > > +
    > > + /*
    > > + * Qualcomm clock drivers by default round clock _up_ if they can't
    > > + * make the requested rate. This is not good for SD. Yell if we
    > > + * encounter it.
    > > + */
    > > + achieved_rate = clk_get_rate(core_clk);
    > > + if (achieved_rate > clock)
    > > + pr_warn("%s: Card appears overclocked; req %u Hz, actual %lu Hz\n",
    > > + mmc_hostname(host->mmc), clock, achieved_rate);
    >
    > How does a warning help?

    The actual fixes are made in the clock drivers, but this seems to be a
    common problem in Qualcomm clock drivers. ...so while this doesn't
    actually fix the problem, it hopefully calls enough attention that
    someone will know to fix it in the clock driver.


    > Also, did you consider setting host->mmc->actual_clock

    That makes sense, though I think logically it's a separate change.
    I'll add it as patch #2 in the series. It's not as trivial as I would
    have thought. ;-)

    -Doug

    >
    > > +
    > > msm_host->clk_rate = clock;
    > > pr_debug("%s: Setting clock at rate %lu at timing %d\n",
    > > - mmc_hostname(host->mmc), clk_get_rate(core_clk),
    > > - curr_ios.timing);
    > > + mmc_hostname(host->mmc), achieved_rate, curr_ios.timing);
    > > }
    > >
    > > /* Platform specific tuning */
    > >
    >

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